Field of the Invention
The invention relates to an evacuable flexible test chamber for a leakage test of a test piece.
Description of Related Art
Such test chambers are film chambers, for example, which comprise walls made of flexible films. Such a test chamber is described in EP 0 741 288 A1. The test piece may be a food package, for example, which is to be tested for tightness. The test piece is placed into the open test chamber. Then the test chamber is closed and evacuated, wherein the flexible walls (film walls) cling to the test piece. Here the term “vacuum” is not to be understood as an absolute vacuum but generally as a lower pressure than that of the atmosphere surrounding the test chamber. The flexible test chamber walls cling to the test piece once the pressure inside the test chamber is lower than that of the atmosphere surrounding the test chamber. Accordingly, the term “evacuate” is also to be understood as the creation of an underpressure and not necessarily as the creation of an absolute vacuum.
When flexible test chambers are closed a problem arises in that due to the elasticity or flexibility of the flexible wall material an amount of gas is enclosed in the test chamber. The quicker the chamber is closed, the larger is the enclosed gas volume since the flexible wall material bulges due to the air resistance and traps an additional gas volume during the closing process. The duration of the evacuation of the test chamber is thus increased. The gain in velocity when the chamber is quickly closed leads to a corresponding loss of velocity during the evacuation thereof since the trapped gas volume must also be evacuated.
It is an object of the invention to provide an improved test chamber and to create an improved method for a leakage test.